In a recent discussion regarding automating e-mails in Access someone brought to my attention that Windows 10 has curl built into it, as of build 1803, which allows sending e-mails, amongst many other things.

This got me curious if it could be a viable replace for say CDO Mail.  As such, I did some research, development and testing and ended up with the following function:

'---------------------------------------------------------------------------------------
' Procedure : curl_SendEmail
' Author    : Daniel Pineault, CARDA Consultants Inc.
' Website   : http://www.cardaconsultants.com
' Purpose   : Send e-mail via Windows 10 curl API
' Copyright : The following is release as Attribution-ShareAlike 4.0 International
'             (CC BY-SA 4.0) - https://creativecommons.org/licenses/by-sa/4.0/
' Req'd Refs: Late Binding  -> none required
' Requirements: Windows 10 V1803 or later
'
' Input Variables:
' ~~~~~~~~~~~~~~~~
' sSTMP             : SMTP server to be used to send the e-mail from
'                       mail.servername.com
' sPortNo           : Port to be used
'                       465, 587
' sAccountUserName  : SMTP server username
' sAccountPassword  : SMTP server password
' sFrom             : E-mail address sending the email
' sTo               : E-mail address of the recipient
' sFile             : Template file of the e-mail message to be sent
'
' Usage:
' ~~~~~~
' ? curl_SendEmail("mail.servername.com", 465, "user@servename.com", "mypassword", _
'                  "me@servername.com", "you@servername2.com", "C:\email.txt")
'
' Revision History:
' Rev       Date(yyyy-mm-dd)        Description
' **************************************************************************************
' 1         2021-06-08              Initial Release
'---------------------------------------------------------------------------------------
Function curl_SendEmail(ByVal sSTMP As String, _
                            ByVal sPortNo As Integer, _
                            ByVal sAccountUserName As String, _
                            ByVal sAccountPassword As String, _
                            ByVal sFrom As String, _
                            ByVal sTo As String, _
                            ByVal sFile As String)
    On Error GoTo Error_Handler
    Dim sCmd                  As String

    'Build the curl command
    '**************************************************
    sCmd = "curl" & _
           " --max-time 10" & _
           " --ssl-reqd" & _
           " --url ""smtps://" & sSTMP & ":" & sPortNo & "/""" & _
           " --user """ & sAccountUserName & ":" & sAccountPassword & """" & _
           " --mail-from """ & sFrom & """" & _
           " --mail-rcpt """ & sTo & """" & _
           " --upload-file """ & sFile & """"
'    Debug.Print sCmd
    'Run the curl command
    '**************************************************
'    CreateObject("Wscript.Shell").Run "cmd /k " & sCmd, 0, False    'Hide window from user / Production
    CreateObject("Wscript.Shell").Run "cmd /k " & sCmd, 1, True  'Display window to user / Development

Error_Handler_Exit:
    On Error Resume Next
    Exit Function

Error_Handler:
    MsgBox "The following error has occured" & vbCrLf & vbCrLf & _
           "Error Number: " & Err.Number & vbCrLf & _
           "Error Source: curl_SendEmail" & vbCrLf & _
           "Error Description: " & Err.Description & _
           Switch(Erl = 0, "", Erl <> 0, vbCrLf & "Line No: " & Erl) _
           , vbOKOnly + vbCritical, "An Error has Occured!"
    Resume Error_Handler_Exit
End Function

Plain Text Email Body

and the email.txt file used as the –outload-file in the function above resembles:

From: SenderEmailAddress
To: RecipientEmailAddress
Subject: Your Subject Line
Date: Tue, 8 Jun 2021 17:18:39 -0400
Content-Language: en-us

Your Actual E-mail Body.

HTMLText Email Body

And for HTML messages you can do something like the following for the –outload-file in the function

From: SenderEmailAddress
To: RecipientEmailAddress
Date: Tue, 8 Jun 2021 17:18:39 -0400
Content-Language: en-us
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/html; charset="UTF-8"
Subject: Your Subject Line

Your Actual HTML E-mail Body.

but you can customize these settings depending on your needs, character set, …

My Conclusions

Although the above is quite simple, I did try countless variations, to try and return the output from the curl command, but nothing worked. I tried outputting to a file using the DOS redirect ‘>textfile’ technique, the clipboard, waiting for the Shell instance to no longer be busy… nothing worked. Even the –output in curl itself failed to generate/populate a text file for me to be able to read. Thus, IMHO, this is yet another poorly implemented utility and offers us no automated way to know if it executed properly or not, unlike say CDO Mail. Thus, it isn’t something I’d recommend in any production system that you need to count on.

I finally managed to get the output redirected and it can be done, not just with the standard command prompt >, but rather 2> (prefixing it with 2 will cause it to redirect/output the stderr rather than stdout). So for instance:

    sCmd = "curl" & _
           " --max-time 10" & _
           " --ssl-reqd" & _
           " --url ""smtps://" & sSTMP & ":" & sPortNo & "/""" & _
           " --user """ & sAccountUserName & ":" & sAccountPassword & """" & _
           " --mail-from """ & sFrom & """" & _
           " --mail-rcpt """ & sTo & """" & _
           " --upload-file """ & sFile & """ 2> C:\Temp\MyOutputFile.txt"

Another option would be 2>&1, but I haven’t tested that one yet.

As to why curl’s –o doesn’t work, no clue!

Also, as explained to me in a forum: “you can never get the SMTP delivery XXX reason code. All you’ll ever get is success/failure about whether the message has queued or not.” somewhat limiting it’s production value IMHO.

One thing I was impressed with was the execution speed of curl. It was lightning fast to send e-mails and also did not suffer from any security pop-ups and other nonsense we now experience with automating Outlook.

I still am not done though and plan on working on this further as I find it very hard to believe Microsoft has implemented such a tool without any way of getting a response from it.

A Few Resources on the Subject

• Everything curl – Sending email
• curl Error Codes